The capability of being able to adjust the output power of an optical transmitter in response to changing conditions within a transmission system and to transfer that output power information to each optical receiver is very important in large optical transmission systems. One such optical system is commonly called the fiber-in-the-loop (FITL) system which will provide optical fiber connections to residential homes. In such systems, there are a large number of optical components in various optical paths, and it is a difficult problem to maintain records which specify the number and type of optical components in each optical path. The number and type of optical components is particularly important in optical transmission systems since attenuation is introduced into the optical transmission path by the optical fibers, splices, connectors, splitters, combiners, etc. The present residential telephone systems illustrate the problems of maintaining accurate records of installed equipment and cables in the residential environment.
One prior art method for correcting this type of situation with respect to the output power level is to manually adjust the optical transmitter and optical receivers by physically adjusting the transmitters and receivers or by entering information into a computer controlling the transmission system and having the computer adjust each individual receiver and transmitter. The problems with a manual adjustment procedure are expense and probability of human errors.
In another prior art method, U.S. Pat. No. 5,060,302 discloses an optical receiver feeding back information to an optical transmitter to adjust the output of the optical transmitter. There are two problems with this prior art solution. First, it only functions where a transmitter is driving a single receiver, and second, it requires an additional optical transmitter and receiver for the feedback path which is expensive. In addition, no provision is made for the adjustment of the optical receiver.
Another prior art method which does not require manual entry of data is disclosed in U.S. Pat. No. 4,295,043. This patent discloses the use of a connector which identifies the length of attached cable by predefined electrical contacts placed on the connector of the cable. Different connectors are used for different lengths of optical fiber when the cable is being assembled. The receiver then automatically adjusts to the cable length based on the electrical contacts and assumes a predefined transmitter output. This method does allow a receiver to adjust for particular lengths of optical fiber in a given transmitter output. However, it does not allow two lengths of optical fiber cable to interconnect the transmitter and receiver. Nor does the method allow for multiple optical receivers to be connected to one optical transmitter.
There exists a need for a method which determines the optimal power output from an optical transmitter on the basis of optical components in the various paths connecting optical receivers to the optical transmitter and which communicates the output of the optical transmitter to each individual optical receiver so that each optical receiver can adjust its sensitivity to match the output of the optical transmitter.
In systems using duplicated optical transmission subsystems, an active one of two optical transmitters transmits to a plurality of receivers. If it becomes necessary for the inactive one of the optical transmitters to become active, the optical receivers must adjust to the difference between signal levels of the two optical transmitters when the optical paths from the optical transmitters to the optical receivers having different attenuations. The time required for the optical receivers to adjust causes data to be lost which can not be tolerated in some systems.
There exist a need for for a method which will allow an inactive optical transmitter to start transmitting to optical receivers without the optical receivers having to adjust for a difference in signal levels.